A known tool for contour milling includes a conventional, indexable milling insert for a contour or end mill. Such a conventional milling insert includes two cutting edges, each one of which has a curved portion connected with a substantially straight portion. The milling insert has, overall, an oval shape as viewed in a planar view. The bottom and side-support surfaces of the milling insert are planar and securing the milling insert is guaranteed principally by the tightening force from a tightening screw, as well as the cooperation between the clearance surfaces of the milling insert and the side-support surfaces of the insert seat. Such known tools, especially those for machining at small cutting depths when only the curved portion of the cutting edge is in engagement with a workpiece, are subject to great axial force components, which tend to press the milling insert out of the insert seat. In turn, this results in the tightening screw being subjected to great forces and there is a risk that the securement may become unstable. At great cutting depths, when the straight portion is also in engagement with the workpiece, this problem does not arise to the same extent, since there is a counteracting force from the part of the workpiece that is machined by the straight portion.
Another known milling tool and milling insert purportedly solve the problem of unstable securements by arranging a recess on the bottom side of the milling insert. The recess cooperates with a projection from the bottom surface of the insert seat. In the mounted state, contact is established on one hand between the bottom side of the milling insert and the bottom surface of the insert seat, and on the other hand between parts of the clearance surface of the milling insert and a plurality of side-support surfaces of the insert seat, as well as between the recess of the milling insert and the projection of the insert seat. However, this solution suffers from the drawback that the abutment becomes overdetermined, i.e., the precise positioning of the cutting edges in relation to the basic body is lost, and the milling insert, in the worst case, wobbles in the insert seat.
Yet another known milling tool and milling insert purportedly solve the problem of unstable securements and inexact positioning by arranging a plurality of recesses on the bottom side of the milling insert. These recesses cooperate with a plurality of projections from the bottom surface of the insert seat. Upon mounting, the milling insert is inserted into the insert seat in such a way that the plural recesses become aligned with the plural projections. In the correct position, a screw can be inserted through a hole and be tightened in a threaded hole such that the bottom side of the milling insert is pressed against the bottom surface, while parts of a clearance surface come into abutment against side-support surfaces in the insert seat. The flanks of the projections come into abutment against the recesses only upon machining, if the milling insert moves somewhat. Although this solution does not suffer from the abutment becoming overdetermined, a certain displacement of the milling insert must be allowed in the insert seat such that the precise positioning of the cutting edges in relation to the basic body is lost.